The proposed research is a renewal of PHS grant RO1DA0182703 "Unapprehended Criminality Among Heroin Users," which was designed to test a method for assessing the nature and extent of unapprehended criminality among heroin users, and to contrast the criminal patterns of the heroin user with those of the non-drug offender. The preliminary findings of the original research indicated that the method was a viable one, and alternative patterns of criminal behavior were apparent. This renewal application seeks to continue the original research with heroin users in the cities of Philadelphia, Pa. and Wilmington, De., to examine the overall criminal careers of a sub-sample of heroin users, to examine the impact of treatment on criminal behavior, and to investigate the structure of drug related fencing operations in the target cities.